1. Field of the Invention
The present invention relates in general to rare gas illumination, and more particularly to systems and methods for the illumination of rare gas tubes.
2. Background
Rare gas tube displays, such as neon signs, are commonly used for advertising and for artistic displays. Historically, these displays were typically illuminated by applying a high voltage signal simultaneously to electrodes at opposite ends of a sealed glass tube containing a rare gas mixture. Hence, the rare gas tubes of these displays were typically either completely "on" or completely "off."
U.S. Pat. No. 4,818,968, which is incorporated by reference herein, discloses a system and method for controlling the propagation of a column of light in a rare gas tube display. The system includes a plurality of rare gas tubes, each having a pair of electrodes disposed at opposite ends of the tube, wherein one of the electrodes is excited to cause a column of light to be emitted from the corresponding rare gas tube starting at a small region at one end of the tube. The excitation is changed to cause the column of light to expand to increasingly larger regions of the tube. Hence, the system creates a light sweeping effect in the rare gas tubes.
The system disclosed in the '968 patent includes appropriate control circuitry to excite the electrodes of the rare gas tubes in a manner that creates the desired light sweeping effect for a particular illumination pattern. A unique control circuit exists for each illumination pattern. Therefore, the control circuitry must be changed to adjust the illumination pattern for a particular rare gas display. The changing of the control circuit can be a time-consuming and cumbersome process.
Furthermore, rare gas tubes generally exhibit certain properties, which complicate the process of creating a predictable, linear light sweeping effect in a particular rare gas display. For example, the capacitance of a particular rare gas tube affects the expansion of a column of light through the rare gas tube. Many displays include curved rare gas tubes for aesthetic and other reasons. The curves of a rare gas tube create capacitance within the tube, which causes nonlinearities in the expansion of a column of light through the curved portions of the rare gas tube. In fact, in a typical configuration, the capacitance of the rare gas tube changes as the column of light propagates through the tube. A capacitance also exists between a rare gas tube and its surrounding environment. The environmental capacitance of a particular rare gas tube can vary widely, depending on the surroundings of the rare gas tube. The variations in capacitance caused by curves within a rare gas tube and by the surroundings of the tube make the process of creating a predictable, linear light sweeping effect in a particular rare gas display more difficult.
In addition, rare gas tubes exhibit certain undesirable properties, which are unrelated to creating a light sweeping effect within the tubes. For example, rare gas tubes typically operate at relatively high voltages, such as about 2000 volts. Therefore, rare gas displays typically use electrical transformers to step up relatively low voltage supply lines to the appropriate voltage level. Conventional transformers that provide the necessary voltage step up can be too large to place near the rare gas display itself. Accordingly, high voltage supply lines are needed for many rare gas displays to carry the high voltage signal from the transformer to the rare gas display. These high voltage supply lines can pose a safety hazard.
Moreover, an illuminated rare gas tube generates an electromagnetic field in the vicinity of the illuminated tube. This electromagnetic field undesirably creates interference, which can affect the illumination of other rare gas tubes located near the illuminated tube. Thus, the electromagnetic interference generated by illuminated rare gas tubes adds complexity and unpredictability to the illumination of rare gas displays having multiple rare gas tubes located near one another.
Additionally, rare gas tubes generally emit certain radio frequency (RF) transmissions when illuminated. These RF transmissions undesirably create interference, which can affect the operation of electronic equipment located in the vicinity of the illuminated rare gas tube. Thus, the interference caused by RF transmissions generated by illuminated rare gas tubes can impose restrictions on the decision regarding where to install a particular rare gas display.